A lunar eclipse happens when Earth moves directly between the Sun and the Moon, and Earth’s shadow falls on the Moon.

Quick Scoop: What Actually Happens

  • The Sun, Earth, and Moon line up in almost a straight line (an alignment called a syzygy).
  • Earth blocks the Sun’s light, so its shadow is cast onto the Moon.
  • Because of Earth’s atmosphere, the Moon usually turns dark red or copper instead of disappearing completely (this is the famous “blood moon”).

Step‑by‑step during a total lunar eclipse

  1. Penumbral phase (P1)
    The Moon enters Earth’s faint outer shadow, the penumbra.
    The darkening is very subtle and often hard to notice with the naked eye.
  1. Partial eclipse begins (U1)
    The Moon moves into Earth’s darker inner shadow, the umbra.
    It looks like a curved “bite” is taken out of the Moon as the shadow creeps across its surface.
  1. Total eclipse begins (U2)
    The entire Moon is now inside the umbra.
    Direct sunlight is blocked, and the Moon starts glowing red, brown, or orange.
  1. Maximum eclipse
    This is the deepest part of the eclipse, when the Moon is fully in Earth’s umbra and at its darkest red.
  1. Total eclipse ends (U3)
    The Moon begins to leave the umbra; one edge brightens as sunlight returns directly to part of its surface.
  1. Penumbral eclipse ends (P4)
    The Moon leaves the penumbra and returns to its normal brightness.

Why the Moon turns red (Blood Moon)

  • Earth’s atmosphere bends (refracts) sunlight into the umbra.
  • Short‑wavelength blue light is scattered away, while longer‑wavelength red light gets bent into the shadow and reflected off the Moon’s surface.
  • To someone on the Moon, this would look like a ring of red sunsets all around Earth’s edge; from Earth, we see the Moon as a dim red disk.

Types of lunar eclipses

  • Total lunar eclipse : The whole Moon passes through Earth’s umbra and usually appears red.
  • Partial lunar eclipse : Only part of the Moon enters the umbra; it looks like a dark chunk is missing.
  • Penumbral lunar eclipse : The Moon only passes through the penumbra; it just looks slightly dimmer and can be easy to miss.

Is it safe and how often?

  • Lunar eclipses are completely safe to watch with the naked eye, binoculars, or a telescope—no filters needed, because you’re just looking at reflected light from the Moon.
  • They do not happen every month because the Moon’s orbit is tilted, so most full moons pass above or below Earth’s shadow instead of through it.

Mini TL;DR:
During a lunar eclipse, the Moon moves into Earth’s shadow, dimming and often turning red because Earth’s atmosphere bends red sunlight into that shadow.